686657971 has 4 divisors (see below), whose sum is σ = 687458200. Its totient is φ = 685857744.

The previous prime is 686657963. The next prime is 686657977. The reversal of 686657971 is 179756686.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 179756686 = 2 ⋅89878343.

It is a cyclic number.

It is not a de Polignac number, because 686657971 - 2³ = 686657963 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (686657977) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 398826 + ... + 400543.

It is an arithmetic number, because the mean of its divisors is an integer number (171864550).

Almost surely, 2^686657971 is an apocalyptic number.

686657971 is a deficient number, since it is larger than the sum of its proper divisors (800229).

686657971 is an equidigital number, since it uses as much as digits as its factorization.

686657971 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 800228.

The product of its digits is 3810240, while the sum is 55.

The square root of 686657971 is about 26204.1594217407. The cubic root of 686657971 is about 882.2266147272.

It can be divided in two parts, 68665 and 7971, that added together give a triangular number (76636 = T₃₉₁).

The spelling of 686657971 in words is "six hundred eighty-six million, six hundred fifty-seven thousand, nine hundred seventy-one".